Multifunctional Catalyst System for Diesel Exhaust Sulfation Prevention
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Solution Overview
Problem
Close coupled selective catalytic reduction (SCR) catalysts based on copper containing zeolitic material with a framework structure of the type CHA can become sulfated over time, leading to insufficient DeNOx and increased nitrous oxide emissions, particularly under CARB regulations.
Innovation Solution
An exhaust gas treatment system comprising a first catalyst with a palladium coating supported on a zirconium-based oxidic material, combined with a zeolitic material having a framework structure of the type CHA, and a second catalyst with a zeolitic material structure of the type CHA, both designed to prevent sulfation and enhance DeNOx performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a close coupled SCR catalyst based on copper containing zeolitic material is used, then the catalyst can treat exhaust gas initially, but it becomes sulfated over time leading to insufficient DeNOx performance
Solution Approach 1:
The patent divides the exhaust gas treatment function into two separate catalysts: a first catalyst (oxidation catalyst) that handles sulfur trioxide conversion, and a second catalyst (SCR catalyst) that handles nitrogen oxide reduction. This segmentation prevents the SCR catalyst from direct exposure to sulfating conditions, thereby maintaining its DeNOx performance over extended service life.
Solution Approach 2:
The first oxidation catalyst acts as an intermediary between the exhaust gas and the second SCR catalyst. It converts sulfur trioxide to sulfur dioxide before the gas reaches the SCR catalyst, preventing sulfation of the zeolitic material while still allowing the SCR catalyst to perform its nitrogen oxide reduction function effectively.
2Object-generated harmful factors
If a close coupled SCR catalyst is used, then initial DeNOx treatment is provided, but nitrous oxide emissions increase after sulfation
Solution Approach 1:
By separating the oxidation function from the SCR function into two distinct catalysts, the system prevents the SCR catalyst from becoming sulfated. This maintains its ability to reduce nitrogen oxides efficiently and convert them to nitrogen and water, thereby reducing nitrous oxide emissions while preserving DeNOx efficiency.
3Reliability
If an oxidation catalyst is added upstream of the SCR catalyst, then sulfation is prevented, but the system complexity increases
Solution Approach 1:
The first catalyst is designed with multi-functionality, serving both as an oxidation catalyst for converting sulfur trioxide and as a potential SCR catalyst itself. This reduces the need for a separate dedicated oxidation catalyst, thereby limiting the increase in system complexity while still preventing sulfation of the main SCR catalyst.
4Power
If the first catalyst contains platinum group metal, then oxidation activity is improved, but cost and complexity increase
Solution Approach 1:
The patent specifies that the first catalyst contains at most 0.0001 weight-% platinum group metal, representing a dramatic reduction from conventional oxidation catalyst formulations. This parameter change maintains sufficient oxidation activity for preventing sulfation while significantly reducing cost and complexity associated with precious metal content.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively regenerates after sulfation, maintaining or increasing DeNOx efficiency while significantly reducing nitrous oxide emissions, thus meeting environmental requirements.
Implementation Method 1
a first catalyst having an inlet end and an outlet end and comprising a coating disposed on a substrate, wherein the coating comprises palladium supported on an oxidic material comprising zirconium
Implementation Method 2
a zeolitic material having a framework structure of the type CHA
Implementation Method 3
close coupled selective catalytic reduction (SCR) catalysts based on copper containing zeolitic material
Implementation Method 4
a zeolitic material comprising one or more of copper and iron
Data Source
AI summary
The present invention relates to an exhaust gas treatment system for treating an exhaust gas stream exiting a diesel engine, wherein said exhaust gas treatment system comprises a first catalyst having an inlet end and an outlet end and comprising a coating disposed on a substrate, wherein the coating comprises palladium supported on an oxidic material comprising zirconium and further comprises one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron; a second catalyst having an inlet end and an outlet end and comprising a coating disposed on a substrate, wherein the coating comprises one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron, wherein at most 0.0001 weight-% of the coating of the second catalyst consists of platinum group metal.